Ectopic mTERT expression in mouse embryonic stem cells does not affect differentiation but confers resistance to differentiation- and stress-induced p53-dependent apoptosis

Mediated roles of oxidative stress and kidney function to leukocyte telomere length and prognosis in chronic kidney disease

BACKGROUND

Few studies have focused on the correlation between leukocyte telomere length (LTL) and cancer-related mortality or identified potential factors that mediate the relationship between LTL and mortality among chronic kidney disease (CKD) patients. Our study aimed to explore the associations between LTL and all-cause and cause-specific mortality and to identify the underlying mediators.

METHODS

CKD patients were obtained from the National Health and Nutrition Examination Survey (NHANES) 1999-2002. Cox regression analysis and restricted cubic spline analysis were used to explore the associations between LTL and all-cause or specific-cause mortality and their nonlinear connections. Stratified analyses were executed to assess the relationships among the different subgroups. The latent mediated factors were confirmed using mediation analysis. Sensitivity analyses were used to evaluate the robustness of our findings.

RESULTS

Longer LTL associated with the lower risk of all-cause mortality, cardiovascular disease (CVD) and cancer-related mortality, and U-shaped relationships were detected. Patients younger than 65 years with greater LTL or who had hypertension had better prognoses. Age and history of hypertension were associated with LTL and overall mortality. In addition, estimated glomerular filtration rate (eGFR), albumin, and total bilirubin mediated the association, and the proportions of indirect effects were 7.81%, 3.77%, and 2.50%, respectively. Six sensitivity analyses confirmed the robustness of our findings.

CONCLUSIONS

This study revealed that LTL was a protective factor for survival among patients with CKD and emphasized the mediating roles of oxidative stress and kidney function.

Adipose-derived stromal/stem cells and extracellular vesicles for cancer therapy

INTRODUCTION

Mesenchymal stromal/stem cells (MSCs) hold great perspective for the therapy of a host of diseases due to regenerative and anti-inflammatory properties by differentiation into diverse cell populations, homing to damaged tissue regions, paracrine effects, and release of extracellular vesicles.

AREAS COVERED

This review describes the isolation, characterization, and potential use of MSCs and ADSCs for benign and malignant diseases. The MSCs may be administered as whole cells or in form of their secretome that is held responsible for most of their beneficial effects. A special constituent of the paracrine components are the extracellular vesicles (EVs) that carry a biologically potent cargo of proteins, cytokines, and RNA.

EXPERT OPINION

The applications of MSCs and ADSCs are amply documented and have been investigated in preclinical models and many unregulated and a few controlled trials. Larger numbers of MSCs and ADSCs can be obtained for allogeneic transfer but imply difficulties including perseverance of the cells in vivo and possible differentiation into harmful cell types. MSC-derived cell-free preparations are easier to handle and manufacture for various applications. Especially, with the help of bioreactors, EVs can be obtained in excessive numbers and preloaded or charged with proteins, cytokines, and regulatory RNA specimen to treat inflammatory diseases and cancer.

Linking stem cells to chromosomal instability

The discovery of a stem cell population in human neoplasias has given a new impulse to the study of the origins of cancer. The tissue compartment in which transformation first occurs likely comprises stem cells, since these cells need to consolidate the short-term and long-term requisites of tissue renewal. Because of their unique role, stem cells have a combination of characteristics that makes them susceptible to genetic damage, transformation, and tumor initiation. One type of genetic damage in particular, chromosomal instability, might affect the stem cell compartment, because it induces an ongoing cycle of DNA damage and alters cellular programming. Here, we will discuss some of the recently described links between SC, chromosomal instability, and carcinogenesis, and outline some of the consequences for oncoimmunology.

The Connection Between Cell Fate and Telomere

Abolition of telomerase activity results in telomere shortening, a process that eventually destabilizes the ends of chromosomes, leading to genomic instability and cell growth arrest or death. Telomere shortening leads to the attainment of the "Hayflick limit", and the transition of cells to state of senescence. If senescence is bypassed, cells undergo crisis through loss of checkpoints. This process causes massive cell death concomitant with further telomere shortening and spontaneous telomere fusions. In functional telomere of mammalian cells, DNA contains double-stranded tandem repeats of TTAGGG. The Shelterin complex, which is composed of six different proteins, is required for the regulation of telomere length and stability in cells. Telomere protection by telomeric repeat binding protein 2 (TRF2) is dependent on DNA damage response (DDR) inhibition via formation of T-loop structures. Many protein kinases contribute to the DDR activated cell cycle checkpoint pathways, and prevent DNA replication until damaged DNA is repaired. Thereby, the connection between cell fate and telomere length-associated telomerase activity is regulated by multiple protein kinase activities. Contrarily, inactivation of DNA damage checkpoint protein kinases in senescent cells can restore cell-cycle progression into S phase. Therefore, telomere-initiated senescence is a DNA damage checkpoint response that is activated with a direct contribution from dysfunctional telomeres. In this review, in addition to the above mentioned, the choice of main repair pathways, which comprise non-homologous end joining and homologous recombination in telomere uncapping telomere dysfunctions, are discussed.

Treatment of diabetes mellitus-induced erectile dysfunction using endothelial progenitor cells genetically modified with human telomerase reverse transcriptase

The efficacy of treatments for diabetes mellitus-induced erectile dysfunction (DMED) is quite poor, and stem cell therapy is emerging as a useful method. In this study, we used endothelial progenitor cells (EPCs) overexpressing human telomerase reverse transcriptase (hTERT) for the treatment of DMED. Rat EPCs were transfected with hTERT (EPCs-hTERT). EPCs-hTERT secreted more growth factors and demonstrated enhanced proliferation and resistance to oxidative stress. Twenty-four male DMED rats were subjected to four treatments: DMED (DMED group), EPCs (EPCs group), EPCs transduced with control lentivirus (EPC-control group) and EPCs-hTERT (EPCs-hTERT group). A group of healthy rats were used as the normal control group. The erectile function in the EPCs-hTERT group was markedly increased compared with the EPCs and EPCs-control groups. The EPCs-hTERT group exhibited more growth factors, smooth muscle content and retained stem cells in penile tissues. The degree of apoptosis and collagen/smooth muscle ratio in penile tissues of the EPCs-hTERT group was considerably reduced. Endothelial nitric oxide synthase (eNOS) expression increased significantly in the EPCs-hTERT group. Taken together, these data showed that the enhanced paracrine effect, resistance to oxidative stress and proliferation of EPCs-hTERT may contribute to the improvements of erectile function in DMED rats.

Electromagnetic Fields and Stem Cell Fate: When Physics Meets Biology

Controlling stem cell (SC) fate is an extremely important topic in the realm of SC research. A variety of different external cues mainly mechanical, chemical, or electrical stimulations individually or in combination have been incorporated to control SC fate. Here, we will deconstruct the probable relationship between the functioning of electromagnetic (EMF) and SC fate of a variety of different SCs. The electromagnetic (EM) nature of the cells is discussed with the emphasis on the effects of EMF on the determinant factors that directly and/or indirectly influence cell fate. Based on the EM effects on a variety of cellular processes, it is believed that EMFs can be engineered to provide a controlled signal with the highest impact on the SC fate decision. Considering the novelty and broad applications of applying EMFs to change SC fate, it is necessary to shed light on many unclear mechanisms underlying this phenomenon.

Spontaneous Single-Copy Loss of TP53 in Human Embryonic Stem Cells Markedly Increases Cell Proliferation and Survival

Genomic aberrations have been identified in many human pluripotent stem cell (hPSC) cultures. Commonly observed duplications in portions of chromosomes 12p and 17q have been associated with increases in genetic instability and resistance to apoptosis, respectively. However, the phenotypic consequences related to sporadic mutations have not been evaluated to date. Here, we report on the effects of a single-copy deletion of the chr17p13.1 region, a sporadic mutation that spontaneously arose independently in several subclones of a human embryonic stem cell culture. Compared to cells with two normal copies of chr17p13.1 ("wild-type"), the cells with a single-copy deletion of this region ("mutant") displayed a selective advantage when exposed to stressful conditions, and retained a higher percentage of cells expressing the pluripotency marker POU5F1/OCT4 after 2 weeks of in vitro differentiation. Knockdown of TP53, which is a gene encompassed by the deleted region, in wild-type cells mimicked the chr17p13.1 deletion phenotype. Thus, sporadic mutations in hPSCs can have phenotypic effects that may impact their utility for clinical applications. Stem Cells 2017;35:872-885.

The Paradox of p53: What, How, and Why?

Unlike the rather stereotypic image by which it was portrayed until not too many years ago, p53 is now increasingly emerging as a multifaceted transcription factor that can sometimes exert opposing effects on biological processes. This includes pro-survival activities that seem to contradict p53's canonical proapoptotic features, as well as opposing effects on cell migration, metabolism, and differentiation. Such antagonistic bifunctionality (balancing both positive and negative signals) bestows p53 with an ideal attribute to govern homeostasis. The molecular mechanisms underpinning the paradoxical activities of p53 may be related to a protein conformational spectrum (from canonical wild-type to "pseudomutant"), diversity of DNA response elements, and/or higher-order chromatin configuration. Altogether, this functional flexibility positions p53 as a transcriptional "super hub" that dictates cell homeostasis, and ultimately cell fate, by governing a hierarchy of other functional hubs. Deciphering the mechanisms by which p53 determines which hubs to engage, and how one might modulate the preferences of p53, remains a major challenge for both basic science and translational cancer medicine.

Establishment of mesenchymal stem cell lines derived from the bone marrow of green fluorescent protein-transgenic mice exhibiting a diversity in intracellular transforming growth factor-β and bone morphogenetic protein signaling

Cytokines and their intercellular signals regulate the multipotency of mesenchymal stem cells (MSCs). The present study established the MSC lines SG-2, -3, and -5 from the bone marrow of green fluorescent protein (GFP)-transgenic mice. These cell lines clearly expressed mouse MSC markers Sca-1 and CD44, and SG-2 and -5 cells retained the potential for osteogenic and adipogenic differentiation in the absence of members of the transforming growth factor (TGF)-β superfamily. By contrast, SG-3 cells only retained adipogenic differentiation potential. Analysis of cytokine and cytokine receptor expression in these SG cell lines showed that bone morphogenetic protein (BMP) receptor 1B was most highly expressed in the SG-3 cells, which underwent osteogenesis in response to BMP, while TGF-β receptor II was most highly expressed in SG-3 and -5 cells. However, it was unexpectedly noted that phosphorylation of Smad 2, a major transcription factor, was induced by TGF-β1 in SG-2 cells but not in SG-3 or -5 cells. Furthermore, TGF-β1 clearly induced the expression of Smad-interacting transcription factor CCAAT/enhancer binding protein-β in SG-2 but not in SG-3 or -5 cells. These results demonstrated the establishment of TGF-β-responsive SG-2 MSCs, BMP-responsive SG-3 MSCs and TGF-β/BMP-unresponsive SG-5 MSCs, each of which was able to be traced by GFP fluorescence after transplantation into in vivo experimental models. In conclusion, the present study suggested that these cell lines may be used to explore how the TGF-β superfamily affects the proliferation and differentiation status of MSCs in vivo.

Ionizing Radiation Perturbs Cell Cycle Progression of Neural Precursors in the Subventricular Zone Without Affecting Their Long-Term Self-Renewal

Damage to normal human brain cells from exposure to ionizing radiation may occur during the course of radiotherapy or from accidental exposure. Delayed effects may complicate the immediate effects resulting in neurodegeneration and cognitive decline. We examined cellular and molecular changes associated with exposure of neural stem/progenitor cells (NSPs) to ¹³⁷Cs γ-ray doses in the range of 0 to 8 Gy. Subventricular zone NSPs isolated from newborn mouse pups were analyzed for proliferation, self-renewal, and differentiation, shortly after irradiation. Strikingly, there was no apparent increase in the fraction of dying cells after irradiation, and the number of single cells that formed neurospheres showed no significant change from control. Upon differentiation, irradiated neural precursors did not differ in their ability to generate neurons, astrocytes, and oligodendrocytes. By contrast, progression of NSPs through the cell cycle decreased dramatically after exposure to 8 Gy (p < .001). Mice at postnatal day 10 were exposed to 8 Gy of γ rays delivered to the whole body and NSPs of the subventricular zone were analyzed using a four-color flow cytometry panel combined with ethynyl deoxyuridine incorporation. Similar flow cytometric analyses were performed on NSPs cultured as neurospheres. These studies revealed that neither the percentage of neural stem cells nor their proliferation was affected. By contrast, γ-irradiation decreased the proliferation of two classes of multipotent cells and increased the proliferation of a specific glial-restricted precursor. Altogether, these results support the conclusion that primitive neural precursors are radioresistant, but their proliferation is slowed down as a consequence of γ-ray exposure.

Microenvironmental regulation of telomerase isoforms in human embryonic stem cells

Recent evidence points to extra-telomeric, noncanonical roles for telomerase in regulating stem cell function. In this study, human embryonic stem cells (hESCs) were cultured in 20% or 2% O2 microenvironments for up to 5 days and evaluated for telomerase reverse transcriptase (TERT) expression and telomerase activity. Results showed increased cell survival and maintenance of the undifferentiated state with elevated levels of nuclear TERT in 2% O2-cultured hESCs despite no significant difference in telomerase activity compared with their high-O2-cultured counterparts. Pharmacological inhibition of telomerase activity using a synthetic tea catechin resulted in spontaneous hESC differentiation, while telomerase inhibition with a phosphorothioate oligonucleotide telomere mimic did not. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed variations in transcript levels of full-length and alternate splice variants of TERT in hESCs cultured under varying O2 atmospheres. Steric-blocking of Δα and Δβ hTERT splicing using morpholino oligonucleotides altered the hTERT splicing pattern and rapidly induced spontaneous hESC differentiation that appeared biased toward endomesodermal and neuroectodermal cell fates, respectively. Together, these results suggest that post-transcriptional regulation of TERT under varying O2 microenvironments may help regulate hESC survival, self-renewal, and differentiation capabilities through expression of extra-telomeric telomerase isoforms.

Stable phenotype and function of immortalized Lin-Sca-1+ cardiac progenitor cells in long-term culture: a step closer to standardization

Putative cardiac progenitor cells (CPCs) have been identified in the myocardium and are regarded as promising candidates for cardiac cell-based therapies. Although two distinct populations of CPCs reached the clinical setting, more detailed studies are required to portray the optimal cell type and therapeutic setting to drive robust cell engraftment and cardiomyogenesis after injury. Owing to the scarcity of the CPCs and the need for reproducibility, the generation of faithful cellular models would facilitate this scrutiny. Here, we evaluate whether immortalized Lin(-)Sca-1(+) CPCs (iCPC(Sca-1)) represent their native-cell counterpart, thereby constituting a robust in vitro model system for standardized investigation in the cardiac field. iCPC(Sca-1) were established in vitro as plastic adherent cells endowed with robust self-renewal capacity while preserving a stable phenotype in long-term culture. iCPC(Sca-1) differentiated into cardiomyocytic-, endothelial-, and smooth muscle-like cells when subjected to appropriate stimuli. The cell line consistently displayed features of Lin(-)Sca-1(+) CPCs in vitro, as well as in vivo after intramyocardial delivery in the onset of myocardial infarction (MI). Transplanted iCPC(Sca-1) significantly attenuated the functional and anatomical alterations caused by MI while promoting neovascularization. iCPC(Sca-1) are further shown to engraft, establish functional connections, and differentiate in loco into cardiomyocyte- and vasculature-like cells. These data validate iCPC(Sca-1) as an in vitro model system for Lin(-)Sca-1(+) progenitors and for systematic dissection of mechanisms underlying CPC subsets engraftment/differentiation in vivo. Moreover, iCPC(Sca-1) can be regarded as a ready-to-use CPCs source for pre-clinical bioengineering studies toward the development of novel strategies for restoration of the damaged myocardium.

Extracting extra-telomeric phenotypes from telomerase mouse models

Telomerase reverse transcriptase (TERT) is the protein component of telomerase and combined with an RNA molecule, telomerase RNA component, forms the telomerase enzyme responsible for telomere elongation. Telomerase is essential for maintaining telomere length from replicative attrition and thus contributes to the preservation of genome integrity. Although diverse mouse models have been developed and studied to prove the physiological roles of telomerase as a telomere- elongating enzyme, recent studies have revealed non-canonical TERT activities beyond telomeres. To gain insights into the physiological impact of extra-telomeric roles, this review revisits the strategies and phenotypes of telomerase mouse models in terms of the extra-telomeric functions of telomerase.

The major reverse transcriptase-incompetent splice variant of the human telomerase protein inhibits telomerase activity but protects from apoptosis

Human telomerase reverse transcriptase (hTERT; the catalytic protein subunit of telomerase) is subjected to numerous alternative splicing events, but the regulation and function of these splice variants is obscure. Full-length hTERT includes conserved domains that encode reverse transcriptase activity, RNA binding, and other functions. The major splice variant termed α+β- or β-deletion is highly expressed in stem and cancer cells, where it codes for a truncated protein lacking most of the reverse transcriptase domain but retaining the known RNA-binding motifs. In a breast cancer cell panel, we found that β-deletion was the hTERT transcript that was most highly expressed. Splicing of this transcript was controlled by the splice regulators SRSF11, HNRNPH2, and HNRNPL, and the β-deletion transcript variant was associated with polyribosomes in cells. When ectopically overexpressed, β-deletion protein competed for binding to telomerase RNA (hTR/TERC), thereby inhibiting endogenous telomerase activity. Overexpressed β-deletion protein localized to the nucleus and mitochondria and protected breast cancer cells from cisplatin-induced apoptosis. Our results reveal that a major hTERT splice variant can confer a growth advantage to cancer cells independent of telomere maintenance, suggesting that hTERT makes multiple contributions to cancer pathophysiology.

Establishment and characterization of the reversibly immortalized mouse fetal heart progenitors

OBJECTIVE

Progenitor cell-based cardiomyocyte regeneration holds great promise of repairing an injured heart. Although cardiomyogenic differentiation has been reported for a variety of progenitor cell types, the biological factors that regulate effective cardiomyogenesis remain largely undefined. Primary cardiomyogenic progenitors (CPs) have a limited life span in culture, hampering the CPs' in vitro and in vivo studies. The objective of this study is to investigate if primary CPs isolated from fetal mouse heart can be reversibly immortalized with SV40 large T and maintain long-term cell proliferation without compromising cardiomyogenic differentiation potential.

METHODS

Primary cardiomyocytes were isolated from mouse E15.5 fetal heart, and immortalized retrovirally with the expression of SV40 large T antigen flanked with loxP sites. Expression of cardiomyogenic markers were determined by quantitative RT-PCR and immunofluorescence staining. The immortalization phenotype was reversed by using an adenovirus-mediated expression of the Cre reconbinase. Cardiomyogenic differentiation induced by retinoids or dexamethasone was assessed by an α-myosin heavy chain (MyHC) promoter-driven reporter.

RESULTS

We demonstrate that the CPs derived from mouse E15.5 fetal heart can be efficiently immortalized by SV40 T antigen. The conditionally immortalized CPs (iCP15 clones) exhibit an increased proliferative activity and are able to maintain long-term proliferation, which can be reversed by Cre recombinase. The iCP15 cells express cardiomyogenic markers and retain differentiation potential as they can undergo terminal differentiate into cardiomyctes under appropriate differentiation conditions although the iCP15 clones represent a large repertoire of CPs at various differentiation stages. The removal of SV40 large T increases the iCPs' differentiation potential. Thus, the iCPs not only maintain long-term cell proliferative activity but also retain cardiomyogenic differentiation potential.

CONCLUSIONS

Our results suggest that the reported reversible SV40 T antigen-mediated immortalization represents an efficient approach for establishing long-term culture of primary cardiomyogenic progenitors for basic and translational research.

Conditionally immortalized mouse embryonic fibroblasts retain proliferative activity without compromising multipotent differentiation potential

Mesenchymal stem cells (MSCs) are multipotent cells which reside in many tissues and can give rise to multiple lineages including bone, cartilage and adipose. Although MSCs have attracted significant attention for basic and translational research, primary MSCs have limited life span in culture which hampers MSCs' broader applications. Here, we investigate if mouse mesenchymal progenitors can be conditionally immortalized with SV40 large T antigen and maintain long-term cell proliferation without compromising their multipotency. Using the system which expresses SV40 large T antigen flanked with Cre/loxP sites, we demonstrate that mouse embryonic fibroblasts (MEFs) can be efficiently immortalized by SV40 large T antigen. The conditionally immortalized MEFs (iMEFs) exhibit an enhanced proliferative activity and maintain long-term cell proliferation, which can be reversed by Cre recombinase. The iMEFs express most MSC markers and retain multipotency as they can differentiate into osteogenic, chondrogenic and adipogenic lineages under appropriate differentiation conditions in vitro and in vivo. The removal of SV40 large T reduces the differentiation potential of iMEFs possibly due to the decreased progenitor expansion. Furthermore, the iMEFs are apparently not tumorigenic when they are subcutaneously injected into athymic nude mice. Thus, the conditionally immortalized iMEFs not only maintain long-term cell proliferation but also retain the ability to differentiate into multiple lineages. Our results suggest that the reversible immortalization strategy using SV40 large T antigen may be an efficient and safe approach to establishing long-term cell culture of primary mesenchymal progenitors for basic and translational research, as well as for potential clinical applications.

p53 in stem cells

p53 is well known as a “guardian of the genome” for differentiated cells, in which it induces cell cycle arrest and cell death after DNA damage and thus contributes to the maintenance of genomic stability. In addition to this tumor suppressor function for differentiated cells, p53 also plays an important role in stem cells. In this cell type, p53 not only ensures genomic integrity after genotoxic insults but also controls their proliferation and differentiation. Additionally, p53 provides an effective barrier for the generation of pluripotent stem cell-like cells from terminally differentiated cells. In this review, we summarize our current knowledge about p53 activities in embryonic, adult and induced pluripotent stem cells.

p53 promotes cellular survival in a context-dependent manner by directly inducing the expression of haeme-oxygenase-1

A variety of cellular insults activate the tumour suppressor p53, leading generally to cell-cycle arrest or apoptosis. However, it is not inconceivable that cellular protective mechanisms may be required to keep cells alive while cell-fate decisions are made. In this respect, p53 has been suggested to perform functions that allow cells to survive, by halting of the cell-cycle, and thus preventing immediate cell death. Nonetheless, the existence of direct pro-survival p53 target genes regulating cellular survival is lacking. We show here evidence for p53-dependent cellular survival in a context-dependent manner. Both mouse and human cells lacking p53 are hypersensitive to hydrogen peroxide (H(2)O(2))-induced cell death compared with their isogenic wild-type counterparts. By contrast, p53(-/-) cells are expectedly resistant to cell death upon exposure to DNA-damaging agents such as cisplatin (CDDP) and etoposide. Although p53 and its classical targets such as p21 and Mdm2 are activated by both H(2)O(2) and CDDP, we found that the expression of haeme-oxygenase-1 (HO-1)-an antioxidant and antiapoptotic protein-was directly induced only upon H(2)O(2) treatment in a p53-dependent manner. Consistently, p53, but not its homologue p73, activated HO-1 expression and was bound to the HO-1 promoter specifically only upon H(2)O(2) treatment. Moreover, silencing HO-1 expression enhanced cell death upon H(2)O(2) treatment only in p53-proficient cells. Finally, H(2)O(2)-mediated cell death was rescued significantly in p53-deficient cells by antioxidant treatment, as well as by bilirubin, a by-product of HO-1 metabolism. Taken together, these data demonstrate a direct role for p53 in promoting cellular survival in a context-specific manner through the activation of a direct transcriptional target, HO-1.

Human telomerase catalytic subunit (hTERT) suppresses p53-mediated anti-apoptotic response via induction of basic fibroblast growth factor

Although human telomerase catalytic subunit (TERT) has several cellular functions including telomere homeostasis, genomic stability, cell proliferation, and tumorigenesis, the molecular mechanism underlying anti-apoptosis regulated by TERT remains to be elucidated. Here, we show that ectopic expression of TERT in spontaneously immortalized human fetal fibroblast (HFFS) cells, which are a telomerase- and p53-positive, leads to increases of cell proliferation and transformation, as well as a resistance to DNA damage response and inactivation of p53 function. We found that TERT and a mutant TERT (no telomerase activity) induce expression of basic fibroblast growth factor (bFGF), and ectopic expression of bFGF also allows cells to be resistant to DNA-damaging response and to suppress activation of p53 function under DNA-damaging induction. Furthermore, loss of TERT or bFGF markedly increases a p53 activity and DNA-damage sensitivity in HFFS, HeLa and U87MG cells. Therefore, our findings indicate that a novel TERT-bFGF axis accelerates the inactivation of p53 and consequent increase of resistance to DNA-damage response.

Rapidly constructed scaffold-free cornea epithelial sheets for ocular surface reconstruction

PURPOSE

To develop a centrifugal cell seeding method for rapid and efficient reconstruction of ocular surface with limbal stem cell deficiency (LSCD) in rabbits.

METHODS

The orthogonal design method was used to optimize centrifugation parameters for cell seeding. Methylthiazol tetrazolium proliferation assay, colony-forming efficiency, and flow cytometry were used to study cell viability. Histology, electron microscopy, and immunocytochemistry were evaluated for centrifugation-constructed cornea epithelial sheets (CCCESs). The rabbit eyes with LSCD were treated with or without CCCES for in vivo evaluation.

RESULTS

The 80.04% attached cells with 98.04% viability were achieved using optimal cell seeding density at 9 × 10(5) cm(-2) with centrifugation at 1800 rpm for 4 min. The 0.4% glycerin was added in the medium to increase the surface tension and osmotic pressure to optimal condition for obtaining higher cell density. The three-layer epithelial sheets were rapid constructed, which displayed the characteristics of normal corneal epithelium. In vivo transplantation, labeled cells of CCCES were detected at 30 days. CCCES reconstructed the LSCD corneal epithelia without conjunctivalization and neovascularation, evidenced by positive K3 and negative K4, Muc5AC.

CONCLUSION

The scaffold-free corneal epithelial sheets were rapidly constructed using optimal centrifugation procedure, which was demonstrated to reconstruct ocular surface with LSCD.

Smad-interacting protein-1 and microRNA 200 family define a nitric oxide-dependent molecular circuitry involved in embryonic stem cell mesendoderm differentiation

OBJECTIVE

Smad-interacting protein-1 (Sip1/ZEB2) is a transcriptional repressor of the telomerase reverse transcriptase catalytic subunit (Tert) and has recently been identified as a key regulator of embryonic cell fate with a phenotypic effect similar, in our opinion, to that reported for nitric oxide (NO). Remarkably, SIP1/ZEB2 is a known target of the microRNA 200 (miR-200) family. In this light, we postulated that Sip1/ZEB2 and the miR-200 family could play a role during the NO-dependent differentiation of mES.

METHODS AND RESULTS

The results of the present study show that Sip1/ZEB2 expression is downregulated during the NO-dependent expression of mesendoderm and early cardiovascular precursor markers, including Flk1 and CXCR4 in mES. Coincidently, members of the miR-200 family, namely miR-429, -200a, -200b, and -200c, were transcriptionally induced in parallel to mouse Tert. This regulation occurred at the level of chromatin. Remarkably, miR-429/miR-200a overexpression or Sip1/ZEB2 knockdown by short hairpin RNA interference elicited a gene expression pattern similar to that of NO regardless of the presence of leukemia inhibitory factor.

CONCLUSIONS

These results are the first demonstrating that the miR-200 family and Sip1/ZEB2 transcription factor are regulated by NO, indicating an unprecedented molecular circuitry important for telomerase regulation and early differentiation of mES.

Enhancement of long-term proliferative capacity of rabbit corneal epithelial cells by embryonic stem cell conditioned medium

Induction of autologous stem cells for directed differentiation has become a predominant method to obtain autologous cells for tissue reconstruction. However, the low inducing efficiency and contamination with other type of cells hinder its clinical utilization. Here we report a novel phenomenon that the corneal epithelial cells maintain long-term proliferative capacity and tissue-specific cell phenotype by factors secreted from murine embryonic stem cells (ESCs). The rabbit corneal epithelial cells grew very well in culture medium with addition of 40% ESC conditioned medium (ESC-CM). These corneal epithelial cells have been serially subcultured for more than 20 passages and maintained high cell purity, cobble-stone-like morphology, enhanced colony forming efficiency, normal diploid, and capacity to regenerate a functional stratified corneal epithelial equivalent. More importantly, these cells did not form tumor, and the cells lost their proliferative capacity after withdrawal of ESC-CM. The long-term proliferative capacity of corneal epithelial cells is partly resulted from enhancement of cell survival and colony formation, and mediated by ectopic expression of telomerase. Our findings indicate that this new ESC-CM culture system can generate low-immunogenic autologous cells sufficiently for use in regenerative medicine.

NFAT5 regulates transcription of the mouse telomerase reverse transcriptase gene

We aimed to clarify the transcription-regulation mechanisms of the mouse telomerase reverse transcriptase gene (mTERT). First, we searched for the promoter region required for transcriptional activation of mTERT and identified an enhancer cis-element (named mTERT-EE) located between -200 and -179bp of the mouse TERT gene (mTERT). EMSA results suggested that nuclear factor of activated T cells (NFAT) member proteins bind to mTERT-EE. We then identified NFAT5 as the factor binding to mTERT-EE and found that it activates the transcription of the mTERT core promoter. The results that siRNA directed against NFAT5 significantly reduced mTERT expression and mTERT core promoter activity and that the expressions of NFAT5 and mTERT were well correlated in various mouse tissues except liver suggest that NFAT5 dominantly and directly regulates mTERT expression. To clarify their functionality further, we investigated the effect of hypertonic stress, a known stimulus affecting the expression and transcriptional activity of NFAT5, on mTERT expression. The result indicated that hypertonic stress activates mTERT transcription via the activation and recruitment of NFAT5 to the mTERT promoter. These results provide useful information about the transcription-regulation mechanisms of mTERT.

TGF-beta induces telomerase-dependent pancreatic tumor cell cycle arrest

Recent studies suggest that transforming growth factor beta (TGF-beta) inhibits telomerase activity by repression of the telomerase reverse transcriptase (TERT) gene. In this report, we show that TGF-beta induces TERT repression-dependent apoptosis in pancreatic tumor, vascular smooth muscle, and cervical cancer cell cultures. TGF-beta activates Smad3 signaling, induces TERT gene repression and results in G1/S phase cell cycle arrest and apoptosis. TERT over-expression stimulates the G1/S phase transition and alienates TGF-beta-induced cell cycle arrest and apoptosis. Our data suggest that telomere maintenance is a limiting factor of the transition of the cell cycle. TGF-beta triggers cell cycle arrest and death by a mechanism involving telomerase deregulation of telomere maintenance.

Transcriptional activity of telomerase complex in CD34- stem cells of cord blood in dependence of preparation time

The aim of the study was to determine whether the expression of telomerase subunits encoding genes changes during the process of cord blood preparation. It should establish if the commonly accepted 24 hours time interval in stem cells kriopreservation procedure significantly influences their immortalization and so decreases the "quality" of cord blood stem cells. Investigation includes 69 women. Spontaneous labour was the inclusion condition. The material was collected at birth after clamping of umbilical cord by direct vasopuncture. CD34- cells were extracted from cord blood (MACS, Miltenyi Biotec; Bisley, Surrey, UK). The expression profile of telomerase activators and inhibitors encoding genes was determined using HG_U133A oligonucleotide microarray (Affymetrix). We used a real-time quantitative RT-PCR assay to quantify the telomerase TERT, hTR and TP1 subunits mRNA copy numbers in CD34- cells in 0, 6, 12 and 24 hours after cord blood collection. We observed significant decrease of numbers of copies of TERTA+B mRNA within the successive hours of observation. Significant decrease of numbers of TERTA mRNA copies was confirmed after 24 hours. However, we observed significant increase of numbers of copies of TERTB mRNA after 6 hours of observation. Similar level was maintained during another 6h. The significantly lower number of copies of TERTB mRNA was observed after 24h. We also observed significant increase of number of copies of TERT mRNA after 6 hours. Number of copies of TERT mRNA significantly decreased after another 6h, remaining, however, on a higher then initial one. The significant lower number of copies of TERT mRNA was observed 24h after delivery. The possible explanation of those results is discussed in the paper.

Effect of human telomerase reverse transcriptase transfection on differentiation in BeWo choriocarcinoma cells

Arrest of proliferation is one of the prerequisites for differentiation of cytotrophoblasts into syncytiotrophoblasts, and thus during differentiation telomerase activity, as well as human telomerase reverse transcriptase (hTERT) expression, is down-regulated. Considering this, it is of interest to investigate whether syncytium formation can be delayed by prolonging the expression of telomerase in cytotrophoblasts. BeWo cells were transfected with pLPC-hTERT retroviral vector and the reverse transcription-polymerase chain reaction analysis for hTERT mRNA concentrations in the transfected cells revealed a several-fold increase in hTERT mRNA compared with the cells transfected with empty vector, and this confirmed that the transfection was successful. An increase in the proliferation, as assessed by bromodeoxyuridine incorporation assay, as well as an increase in mRNA and protein concentration of various cyclins and proliferating cell nuclear antigen, was noticed. The effect of hTERT transfection was also assessed after the addition of forskolin to induce differentiation and it was observed that cell-cell fusion was delayed and differentiation did not occur in hTERT-transfected cells. However, the effects seen were only transient as stable transfection was not possible and the cells were undergoing apoptosis after 72 h, which suggested that apart from hTERT other factors might be important for immortalization of BeWo cells.

Interfacing Sca-1(pos) mesenchymal stem cells with biocompatible scaffolds with different chemical composition and geometry

An immortalized murine mesenchymal stem cell line (mTERT-MSC) enriched for Lin^neg/Sca-1^pos fraction has been obtained through the transfection of MSC with murine TERT and single-cell isolation. Such cell line maintained the typical MSC self-renewal capacity and continuously expressed MSC phenotype. Moreover, mTERT-MSC retained the functional features of freshly isolated MSC in culture without evidence of senescence or spontaneous differentiation events. Thus, mTERT-MSC have been cultured onto PLA films, 30 and 100 μm PLA microbeads, and onto unpressed and pressed HYAFF-11 scaffolds. While the cells adhered preserving their morphology on PLA films, clusters of mTERT-MSC were detected on PLA beads and unpressed fibrous scaffolds. Finally, mTERT-MSC were not able to colonize the inner layers of pressed HYAFF-11. Nevertheless, such cell line displayed the ability to preserve Sca-1 expression and to retain multilineage potential when appropriately stimulated on all the scaffolds tested.

Telomerase regulation in hematological cancers: a matter of stemness?

Human telomerase is a nuclear ribonucleoprotein enzyme complex that catalyzes the synthesis and extension of telomeric DNA. This enzyme is highly expressed and active in most malignant tumors while it is usually not or transiently detectable in normal somatic cells, suggesting that it plays an important role in cellular immortalization and tumorigenesis. As most leukemic cells are generally telomerase-positive and have often shortened telomeres, our understanding of how telomerase is deregulated in these diseases could help to define novel therapies targeting the telomere/telomerase complex. Nonetheless, considering that normal hematopoietic stem cells and some of their progeny do express a functional telomerase, it is tempting to consider such an activity in leukemias as a sustained stemness feature and important to understand how telomere length and telomerase activity are regulated in the various forms of leukemias.

The R246S hot-spot p53 mutant exerts dominant-negative effects in embryonic stem cells in vitro and in vivo

p53 is the most frequently mutated tumour-suppressor gene in human cancers. Mutant p53 is thought to contribute to carcinogenesis by the acquisition of gain-of-function properties or through the exertion of dominant-negative (DN) effects over the remaining wild-type protein. However, the context in which the DN effects are observed is not well understood. We have therefore generated `knock-in' mouse embryonic stem (ES) cells to investigate the effects of expressing a commonly found hot-spot p53 mutant, R246S – the mouse equivalent of human R249S, which is associated with hepatocellular carcinomas. We demonstrate here that R246S mutant p53 exhibits DN effects with respect to target gene expression, cell survival and cell cycle arrest both in cells that are in the undifferentiated state and upon differentiation. The knock-in cells contain higher levels of p53 that localizes to the nucleus even in the absence of genotoxic stress and yet remains non-functional, reminiscent of mutant p53 found in human tumours. In a model based on carbon-tetrachloride-induced liver injury, these cells were consistently highly tumorigenic in vivo, similar to p53–/– cells and in contrast to both p53+/+ and p53+/– ES cells. These data therefore indicate that the DN effects of mutant p53 are evident in the stem-cell context, in which its expression is relatively high compared with terminally differentiated cells.

Defective MHC class I antigen surface expression promotes cellular survival through elevated ER stress and modulation of p53 function

Defects in Major Histocompatibility class I cell surface expression is thought to allow escape of tumor cells from immune surveillance. Hitherto, it is unclear whether this deficiency confers immune-independent survival advantage. We show here that class I cell surface expression deficiency due to defects in beta2 microglobulin or the transporter-associated with antigen processing (TAP) results in resistance to apoptosis in response to various cytotoxic signals. Reduced apoptosis correlated with altered p53 activation, which was due to compromised nuclear translocation of p53. Binding of p53 to glycogen synthase kinase-3beta (GSK3beta), which is known to phosphorylate and lead to cytoplasmic sequestration of p53, was enhanced in these cells. Consistently, endoplasmic reticulum (ER) stress, which promotes binding of p53 to GSK3beta was constitutively elevated in the absence of class I cell surface expression. Taken together, the results suggest a non-immunological causal role for defective class I cell surface expression in regulating cellular survival in a p53-dependent manner, through the upregulation of ER stress, which could be another mechanism leading to carcinogenesis.

Different patterns of in vivo pro-oxidant states in a set of cancer- or aging-related genetic diseases

A comparative evaluation is reported of pro-oxidant states in 82 patients with ataxia telangectasia (AT), Bloom syndrome (BS), Down syndrome (DS), Fanconi anemia (FA), Werner syndrome (WS), and xeroderma pigmentosum (XP) vs 98 control donors. These disorders display cancer proneness, and/or early aging, and/or other clinical features. The measured analytes were: (a) leukocyte and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), (b) blood glutathione (GSSG and GSH), (c) plasma glyoxal (Glx) and methylglyoxal (MGlx), and (d) some plasma antioxidants [uric acid (UA) and ascorbic acid (AA)]. Leukocyte 8-OHdG levels ranked as follows: WS>BS approximately FA approximately XP>DS approximately AT approximately controls. Urinary 8-OHdG levels were significantly increased in a total of 22 patients with BS, FA, or XP vs 47 controls. The GSSG:GSH ratio was significantly increased in patients with WS and in young (< or =15 years) patients with DS or with FA and decreased in older patients with DS or FA and in AT, BS, and XP patients. The plasma levels of Glx and/or MGlx were significantly increased in patients with WS, FA, and DS. The UA and AA levels were significantly increased in WS and DS patients, but not in AT, FA, BS, nor XP patients. Rationale for chemoprevention trials is discussed.

A key role for telomerase reverse transcriptase unit in modulating human embryonic stem cell proliferation, cell cycle dynamics, and in vitro differentiation

Embryonic stem cells (ESC) are a unique cell population with the ability to self-renew and differentiate into all three germ layers. Human ESC express the telomerase reverse transcriptase (TERT) gene and the telomerase RNA (TR) and show telomerase activity, but TERT, TR, and telomerase are all downregulated during the differentiation process. To examine the role of telomerase in human ESC self-renewal and differentiation, we modulated the expression of TERT. Upregulation of TERT and increased telomerase activity enhanced the proliferation and colony-forming ability of human ESC, as well as increasing the S phase of the cell cycle at the expense of a reduced G1 phase. Upregulation of TERT expression was associated with increases in CYCLIN D1 and CDC6 expression, as well as hyperphosphorylation of RB. The differentiated progeny of control ESC showed shortening of telomeric DNA as a result of loss of telomerase activity. In contrast, the differentiated cells from TERT-overexpressing ESC maintained high telomerase activity and accumulated lower concentrations of peroxides than wild-type cells, implying greater resistance to oxidative stress. Although the TERT-overexpressing human ESC are able to form teratoma composed of three germ layers in vivo, their in vitro differentiation to all primitive and embryonic lineages was suppressed. In contrast, downregulation of TERT resulted in reduced ESC proliferation, increased G1, and reduced S phase. Most importantly, downregulation of TERT caused loss of pluripotency and human ESC differentiation to extraembryonic and embryonic lineages. Our results indicate for the first time an important role for TERT in the maintenance of human ESC pluripotency, cell cycle regulation, and in vitro differentiation capacity.

Phosphorylation at carboxyl-terminal S373 and S375 residues and 14-3-3 binding are not required for mouse p53 function

gamma-Irradiation-mediated ataxia telangiectasia mutated (ATM)-dependent dephosphorylation of serine 376 (S376) at the carboxyl terminus of human p53 results in the exposure of the 14-3-3 consensus-binding site, which includes serine 378 (S378). 14-3-3 binding potentiates p53's DNA-binding ability and causes G(1) arrest. Moreover,endoplasmic reticulum stress-mediated S376 phosphorylation was shown to localize human p53 in the cytoplasm. Although many functions are conserved between human and mouse p53, the functional relevance of S376 and S378 mouse equivalents is not clear. We report here that gamma-irradiation does not lead to 14-3-3 binding to mouse p53. Mouse p53 mutants, such as S373A/D (the equivalent of human S376), S375A/D (the equivalent of human S378), and combinatorial double mutants, were not impaired in their ability to transactivate p53-dependent target genes and were capable of inducing G(1) arrest as efficiently as wild-type p53. Consistently, all mutant p53s were as potent as wild-type mouse p53 in inhibiting cellular colony formation. Furthermore, mouse S373A/D mutants were not defective in cytoplasmic localization in response to endoplasmic reticulum stress. Together, the data suggest that despite a high homology with human p53, neither phosphorylation status at S373 and S375 nor 14-3-3 binding may be a critical event for mouse p53 to be functional.

Mechanisms of action of TGF-beta in cancer: evidence for Smad3 as a repressor of the hTERT gene

Transforming growth factor-beta (TGF-beta) induces cell differentiation and suppresses cell proliferation, but the mechanisms underlying the actions of TGF-beta remain to be fully elucidated. Recent studies suggest that TGF-beta suppresses neoplastic cell development by employing Smad3 protein to repress the gene of human telomerase reverse transcriptase (hTERT). In human breast cancer cells, TGF-beta induces rapid phosphorylation and subsequent entry of Smad3 into the nucleus. In the nucleus, Smad3 binds to the hTERT gene promoter directly and inhibits hTERT gene transcription activity. By interacting with c-myc, Smad3 also represses the c-myc gene. Thus, TGF-beta prevents continuous cell proliferation by switching off telomerase activity through Smad3 repression of the hTERT gene and the action of c-myc. Modulating the interface between Smad3 and the hTERT gene, and the potential feedback loop from telomeres to Smad3 via Smurf2, may represent a novel approach to regulate cell lifespan of proliferation.

Regeneration in pig livers by compensatory hyperplasia induces high levels of telomerase activity

Background

Several highly proliferative human cells transiently activate telomerase, a ribonucleoprotein with reverse transcriptase activity, to counterbalance replication-associated telomere erosion and to increase stress resistance. Quiescent human hepatocytes exhibit very low or undetectable levels of telomerase activity. However, hepatocytes display a remarkable proliferative capability following liver injury. To investigate whether liver regeneration by compensatory hyperplasia is associated with telomerase activation, we measured telomerase activity in pig livers after 70 to 80% partial hepatectomy using a fully quantitative real-time telomeric repeat amplification protocol. In contrast to commonly studied inbred laboratory mouse strains, telomere length and telomerase activity in porcine tissues are comparable to humans.

Results

Following partial hepatectomy, histology revealed mitotic hepatocytes as marker for compensatory hyperplasia. As expected, there was no induction of inflammation. Telomerase activity increased significantly showing the highest levels (5-fold upregulation) in pigs treated with partial hepatectomy and hepatic decompression. Moreover, telomerase activity significantly correlated to the number of mitotic hepatocytes.

Conclusion

Our data demonstrate telomerase activation in liver regeneration by compensatory hyperplasia in a large animal model with telomere biology comparable to humans. Telomerase activation may constitute a mechanism to protect proliferating liver cells against telomere shortening and oxidative stress.

Ectopic telomerase expression inhibits neuronal differentiation of NT2 neural progenitor cells

There is significant interest in the potential use of telomerase-immortalized cells in transplantation to replace neurons lost to neurodegenerative diseases and other central nervous system injuries. Neural progenitor cells (NPCs) transduced with human telomerase reverse transcriptase (hTERT), the catalytic component of telomerase, have the potential both to proliferate indefinitely in vitro and to respond to differentiation signals necessary for generating appropriate cells for transplantation. The purpose of this study was to evaluate the differentiation of neurons from NT2 cells, a model NPC cell line, following hTERT transduction. RT-PCR and telomerase activity data demonstrated that persistent exogenous hTERT expression significantly inhibited the differentiation of neurons from NT2 cells. Following retinoic acid induced differentiation, hTERT-NT2 cells produced only one fourth of the neurons generated by parental and vector-control cells. A differentiation-inhibiting effect of constitutive telomerase activity has not been reported previously in other hTERT-transduced progenitor cell lines, implying a unique role for telomerase in the proliferation and differentiation of NPCs that have tumorigenic potential. Elucidating the mechanism responsible for this effect may aid in understanding the potential role of telomerase activity in the tumorigenicity of NPCs, as well as in optimizing the production of safe, telomerase-engineered, transplantable neurons.

Cancer-derived p53 mutants suppress p53-target gene expression--potential mechanism for gain of function of mutant p53

Tumour-derived p53 mutants are thought to have acquired 'gain-of-function' properties that contribute to oncogenicity. We have tested the hypothesis that p53 mutants suppress p53-target gene expression, leading to enhanced cellular growth. Silencing of mutant p53 expression in several human cell lines was found to lead to the upregulation of wild-type p53-target genes such as p21, gadd45, PERP and PTEN. The expression of these genes was also suppressed in H1299-based isogenic cell lines expressing various hot-spot p53 mutants, and silencing of mutant p53, but not TAp73, abrogated the suppression. Consistently, these hot-spot p53 mutants were able to suppress a variety of p53-target gene promoters. Analysis using the proto-type p21 promoter construct indicated that the p53-binding sites are dispensable for mutant p53-mediated suppression. However, treatment with the histone deacetylase inhibitor trichostatin-A resulted in relief of mutant p53-mediated suppression, suggesting that mutant p53 may induce hypo-acetylation of target gene promoters leading to the suppressive effects. Finally, we show that stable down-regulation of mutant p53 expression resulted in reduced cellular colony growth in human cancer cells, which was found to be due to the induction of apoptosis. Together, the results demonstrate another mechanism through which p53 mutants could promote cellular growth.

TGF-beta and cancer: is Smad3 a repressor of hTERT gene?

Transforming growth factor beta (TGF-beta) carries out tumor suppressor activity in epithelial and lymphoid cells, whereas telomerase is required for most cancers. Although the molecular mechanisms by which TGF-beta acts as a tumor suppressor are yet to be fully established, a link between TGFb and its tumor suppressor activity by telomerase has been suggested. Recently, we have noted a novel mode of action for TGF-beta through which human telomerase reverse transcriptase (hTERT) gene is repressed in immortal and neoplastic cells, confirming that one of the mechanisms underlying TGF-beta suppression of tumor growth may be through inhibiting hTERT gene transcription. Moreover, the inhibition of hTERT gene by TGF-beta suggests a cis action of the TGF-beta signaling molecule Smad3 on hTERT promoter directly. This article examines our current understanding and investigation of TGF-beta regulation of telomerase activity, and presents a model in which Smad3 participates in regulating hTERT gene transcription by acting as a repressor directly. Engineering the interface between Smad3 and hTERT gene may lead to a new strategy to inhibit telomerase activity in cancer.

The codon 72 polymorphism-specific effects of human p53 are absent in mouse cells: implications on generation of mouse models

Human p53, unlike mouse p53, contains a polymorphic site at codon 72 in exon 4 encoding either an arginine amino acid (72R) or a proline residue (72P). The 72R form was shown to induce apoptosis better than the 72P form, partly owing to its ability to efficiently bind to the nuclear-export protein CRM1 and localize to the mitochondria. This polymorphism has also been associated with cancer predisposition and chemo-sensitivity. Further understanding of the in vivo significance of this polymorphism in carcinogenesis requires the generation of mouse models. We have thus evaluated if the polymorphism-specific effects of human p53 are retained in mouse cells. Though being transcriptionally active, both the human polymorphs were found to have lost their ability to differentially suppress growth and bind to CRM1 or MDM2 in mouse cells. Moreover, chimaeric proteins containing mouse exons 2-3 and human exons 4-11 have also lost the polymorphism-specific effects in human cells, suggesting that human exons 2-3 are important in regulating the polymorphism-specific effects. Furthermore, human p53 and the various chimaeric proteins were generally less effective in inhibiting growth of mouse cells compared to mouse p53, suggesting that mouse p53 is more potent than human p53 in suppressing growth, partly due to enhanced binding of MDM2 to human p53. The data together suggest that mouse cells may not provide an appropriate environment for the manifestation of the polymorphism-specific functional differences of human p53, and hence, cautions against the expression of full-length or chimaeric p53 proteins in mice to study the effects of the polymorphism.

Challenges and prospects for the establishment of embryonic stem cell lines of domesticated ungulates

Embryonic stem (ES) cell lines provide an invaluable research tool for genetic engineering, developmental biology and disease models. These cells can be maintained indefinitely in culture and yet maintain competence to produce all the cells within a fetus. While mouse ES cell lines were first established over two decades ago and primate ES cells in the 1990 s, validated ES cell lines have yet to be established in ungulates. Why competent, pluripotent ES cells can be established from certain strains of mice and from primates, and not from cows, sheep, goats or pigs is an on-going topic of interest to animal reproduction scientists. The identification of appropriate stem cell markers, functional cytokine pathways, and key pluripotency-maintaining factors along with the release of more comprehensive bovine and porcine genomes, provide encouragement for establishment of ungulate ES cell lines in the near future.

Transforming growth factor beta suppresses human telomerase reverse transcriptase (hTERT) by Smad3 interactions with c-Myc and the hTERT gene

Telomerase underpins stem cell renewal and proliferation and is required for most neoplasia. Recent studies suggest that hormones and growth factors play physiological roles in regulating telomerase activity. In this report we show a rapid repression of the telomerase reverse transcriptase (TERT) gene by transforming growth factor beta (TGF-beta) in normal and neoplastic cells by a mechanism depending on the intracellular signaling protein Smad3. In human breast cancer cells TGF-beta induces rapid entry of Smad3 into the nucleus where it binds to the TERT gene promoter and represses TERT gene transcription. Silencing Smad3 gene expression or genetically deleting the Smad3 gene disrupts TGF-beta repression of TERT gene expression. Expression of the Smad3 antagonist, Smad7, also interrupts TGF-beta-mediated Smad3-induced repression of the TERT gene. Mutational analysis identified the Smad3 site on the TERT gene promoter, mediating TERT repression. In response to TGF-beta, Smad3 binds to c-Myc; knocking down c-Myc, Smad3 does not bind to the TERT gene, suggesting that c-Myc recruits Smad3 to the TERT promoter. Thus, TGF-beta negatively regulates telomerase activity via Smad3 interactions with c-Myc and the TERT gene promoter. Modifying the interaction between Smad3 and TERT gene may, thus, lead to novel strategies to regulate telomerase.

Adenoviral Human Telomerase Reverse Transcriptase Dramatically Improves Ischemic Wound Healing Without Detrimental Immune Response in an Aged Rabbit Model

Chronic ischemic wounds are major clinical problems, and are especially prevalent in elderly patients. Management of these wounds costs billions of dollars annually in the United States. Because of the severe impairment in tissue repair, ischemic wounds among the aged are major challenges for physicians. For example, transforming growth factor-beta1 stimulates healing of young patients' ischemic wounds, but it is totally ineffective in treating the ischemic wounds of aged patients. Therefore, our goal is to develop a better therapeutic strategy for elderly patient ischemic wounds. Because human telomerase reverse transcriptase (hTERT) has emerged as having a role in promoting cell proliferation, we hypothesized that hTERT overexpression may improve ischemic wound healing in the elderly. We successfully tested this hypothesis by demonstrating for the first time that gene delivery of hTERT by adenovirus (Ad-hTERT) dramatically improved ischemic wound healing in an aged rabbit model. Importantly, our histological data indicate that no deleterious immune response was induced in the aged rabbits. This finding has broad implications for the field of gene therapy because the foremost obstacle in the use of adenoviral vectors for gene therapy is that they provoke strong innate and adaptive immune responses in the host. Moreover, Ad-hTERT significantly improved survival of primary rabbit dermal fibroblasts that were treated with hypoxia and hydrogen peroxide (oxidative stress). This model is clinically relevant because it simulates the ischemia cycle of an ischemia-reperfusion injury, which can lead to stroke, myocardial infarction, and other tissue injuries. We conclude that Ad-hTERT is an effective and novel approach to treating the ischemic wounds of elderly patients.

Complicated RNA splicing of chicken telomerase reverse transcriptase revealed by profiling cells both positive and negative for telomerase activity

Telomerase reverse transcriptase (TERT) is an essential component of the telomerase ribonucleoprotein complex which maintains telomeres. The objective of this study was to investigate chicken TERT (cTERT) alternative RNA splicing profiles of samples varying for telomerase activity and immortalization parameters. These included systems both in vivo (gastrula embryo, embryo and adult liver) and in vitro (chicken embryo fibroblasts (CEFs) and DT40 cells). Nineteen cTERT variants were discovered, which were generated through exon skipping, intron retention, and alternative usage of splice donor and acceptor sites. Three variants were predicted to introduce in-frame mutations, whereas the others were predicted to have premature termination codons. The number of cTERT variants detected ranged from 10 in adult liver to 13 in CEFs. One variant (V4) was found in all samples and was predicted to generate a truncated protein lacking telomerase catalytic activity. Interestingly, the standard TERT expected from the full-length transcript was expressed not only in telomerase-positive, but also in telomerase-negative samples. The complicated expression profiles of cTERT in various cell systems suggest that sophisticated regulatory pathways are involved in cTERT pre-mRNA editing. Further, these results support the body of increasing evidence that alternative splicing of TERT, both in human and chicken, contributes to telomerase activity regulation.